For years, people have used remote sensors in hostile environments, placing sensors in locations where human or manual data collection is unattainable or too costly. In toxic and environmentally dangerous environments, for example, remote sensors may provide an effective way of measuring data that might otherwise go unmeasured. In space-constrained environments, remote sensors may be useful in reaching otherwise unreachable locations.
Despite the deployment of remote sensors in certain applications, many applications are incompatible with certain types of remote sensors, or remote sensors altogether. Electrically-powered remote sensors, for example, are not used in environments where electrical conduction can lead to sensor damage or environmental damage. In an aircraft, for example, lightning strikes can be dangerous and damage on-board electronics such as those that would be used in and to power electronic sensors. This lightning problem may be exacerbated by the light-weight, less shielding composite structures used with increasing regularity in modern aircraft. In a spacecraft, for example, a lightning strike could harm the electronic sensors used to monitor mission critical launch conditions. In fact, lightning damage has resulted in some infamous losses of spacecraft, including the Atlas G-Centaur AC-67 space mission. Lightning also nearly caused the astronauts to abort the Apollo 12 spacecraft launch, when a lightning strike triggered electrical warning signals and disabled telemetry systems. Moreover, the problem of spiking is not limited to lightning, as other high voltages would be hazardous if combined with electrically powered sensors in certain environments, such as inside fuel tanks where there is the potential for an igniting hazard through short circuits in the electrical wiring.
Not only are electrical field and voltage surges problematic, high-power microwave radiation can also limit the use of certain types of sensors. For example, it is difficult to use electronic sensors to monitor high-power phased array radar systems because of electromagnetic field interference. High voltage isolation is a limiting factor for high-voltage, power-line sensor applications, as well.
Whereas electrically-powered sensors may be incompatible with certain environments, optically-powered sensors may show potential. In aircraft, for example, an optically powered sensor could protect against lightning, electric fields and discharges, and other electronic interference.
Yet, despite the theoretical attractiveness of optically-powered sensors, there are numerous limitations affecting their deployment. One problem is the lack of efficient and effective methods to optically power multiple sensors. Some powering techniques convert an optical energy on a fiber to electrical power at the sensor. However, the techniques are only used to power a single sensor, unless a fiber optic splitter or multiplexing device is used, thereby adding to device cost, weight, and complexity. Furthermore, remote powering techniques can require a minimum of two fibers for each sensor—one fiber to optically power the sensor, another fiber to receive sensor data. Even the commercially-available pie-wedge photonic power converters suggested by some (in addition to being expensive) would require a fiber bundle to receive data from multiple sensors. In short, the present techniques for optically powering remote sensors would require multiple fibers or a large fiber bundle if multiple sensors were to be deployed, and this requirement is undesirable in space- or weight-constrained systems such as an aircraft, or spacecraft.
It is desirable to have a way of optically powering multiple sensors that may be placed remotely from one another, and to do so in a way that remote sensed signals may be communicated to a centralized analyzer via the same fibers used for powering the sensors.